Water-soluble polymers have traditionally been handled in their dry, particulate form. Problems associated with dry polymers include undesirable dust generation, poor dispersibility when added to aqueous systems, and undesirably long dissolution times.
The dust associated with dry, particulate water-soluble polymers presents the same conventional handling problems as are encountered with similar particulate materials. One major concern is the possibility of dust explosions.
Water-soluble polymers are hygroscopic and absorb water from the air, which can cause agglomeration of the particles. Such agglomerated particles are very difficult, if not impossible, to disperse in an aqueous system.
When added to aqueous systems, water-soluble polymers tend to agglomerate to form clumps. Agglomeration can be reduced in many cases by adding the polymer to the aqueous system slowly with agitation. Slow dissolution substantially reduces the speed of manufacturing operations.
For the above reasons, plant operators desire a fast, effective and simple way of incorporating water-soluble polymers into an aqueous system.
Bishop et al, in U.S. Pat. No. 4,726,912, describe a hydrocarbon oil based suspension of carboxymethylcellulose which upon contact with aqueous fluids facilitates dispersion of the carboxymethylcellulose in the water phase. They state that use of carboxymethylcellulose having a moisture content of 12 to 25 weight percent permits the formation of stable suspensions of carboxymethylcellulose in a hydrocarbon oil which additionally contains anionic surfactants and suspending agents. This suspension can be transported to plants where the carboxymethylcellulose is to be used.
Pickens et al, in U.S. Pat. No. 4,312,675, describe high concentration polymer slurries containing up to 65 weight % of a hydrophilic colloid in a hydrophobic solvent.
Colegrove, in U.S. Pat. No. 3,894,879, states that water-soluble xanthan gum can be prepared as a highly concentrated suspension in alcohol-water carriers using hydroxyalkyl cellulose derivatives as the suspending agents, and, in U.S. Pat. No. 3,894,880, states that water-soluble alginates can be prepared as highly concentrated pumpable suspension in alcohol-water carriers using xanthan gum as a suspending agent.
Braun et al, in U.S. Pat. No. 4,325,861, describe a nonaqueous composition adapted to provide, upon dilution with water, a solution containing a high molecular weight water-soluble polymer. The nonaqueous composition comprises (a) a particulate water-soluble polymer, (b) a water-insoluble, organic liquid vehicle, (c) an inert, nonionic surfactant, and (d) an inert thickening agent.
Organic based systems, such as those described above, are not suitable for many applications. The organic materials present in such systems are undesirable in many end use applications. Further, the organic media are flammable and expensive. Accordingly, a water-based system has been desired.
Burge, in U.S. Pat. No. 4,069,062, describes a method of incorporating water-soluble polymers into mortar or concrete by dispersing an unswollen, water-soluble, swellable polymer in an aqueous solution of a water-soluble salt or organic solvent in which said substance is only partially soluble or totally insoluble and, then, mixing this dispersion into the mortar or concrete. Burge states that the salt or organic solvent serves to prevent dissolution and swelling of the polymeric substance. Specifically mentioned are aqueous solutions of NaCl, Na.sub.2 SO.sub.4, MgSO.sub.4, Al.sub.2 (SO.sub.4).sub.3 and NaH.sub.2 PO.sub.4, alcohol and glycol. Bentonite is used as a stabilizer.
Girg et al, in U.S. Pat. No. 4,283,229, disclose that a stable suspension can be prepared by adding a nonionic, water-soluble cellulose ether derivative to a solution of an electrolyte if alumina is added to the suspension. Suitable electrolytes are described to include metal or ammonium salts of mineral acids or organic acids, especially salts which contain an alkali metal ion, an alkaline earth metal ion, an earth metal ion, or a zinc, copper, iron or manganese ion as the cation, and a sulfate, carbonate, silicate, sulfite, halide, phosphate, nitrate, nitrite, acetate, formiate, tartate, or citrate ion, including their hydrogen salts, as the anion. It is stated that stable solutions of the cellulose derivatives are only formed when alumina is added to the system.
None of these aqueous systems provides a suitable method of dispersing high concentrations of water-soluble polymer in an aqueous system, as gels tend to form at high water-soluble polymer concentrations and the products will not flow or be readily pumpable. Accordingly, users of water-soluble polymers desire a stable, concentrated, aqueous water-soluble polymer suspension that can be used to incorporate water-soluble polymers in aqueous solutions readily, without formation of agglomerates or clumps, and which may be handled without the problems associated with dry powder water-soluble polymers.